The prior art discloses a distributed power supply system in which multiple variable power generators and multiple load devices are connected to a DC bus. The variable power generators used in the system are, for example, photovoltaic power generators and wind power generators. When the voltage of the DC bus is lowered, the system selectively cuts off power supply to the selected load devices with low importance in a step-by-step-manner according to the voltage level of the DC bus.
On the other hand, with an aim to apply to the smart grid, research and development has been conducted on HVDC (High Voltage Direct Current) power transmission at a voltage level of about 380V. In such a large-scale power transmission system, it is desirable that each of the load devices autonomously control supply of input voltage to itself.
For example, the prior art discloses a voltage conversion device which is capable of, when detecting drop of input voltage to its voltage conversion circuit, decreasing supply of input current to the voltage conversion circuit so as to lower power supplied to a load device by the voltage conversion circuit.